Crust:

1 1/2 cups graham cracker crumbs
3 tbsp. sugar
1/3 cup butter, melted

Preheat oven to 350°F. Combine cracker crumbs, sugar and butter. Reserve 1/4 cup of this crumb mixture and press the rest into a 9-inch pie pan. Bake at 350°F for 8 minutes. Allow to cool.

Filling:

3 tsp. cornstarch
2/3 cup sugar
1/4 cup water, cold
2 pounds grapes, seedless (green), with stems removed
1 tbsp. lemon juice

Dissolve cornstarch and sugar in cold water in saucepan. Add grapes and bring to boil, stirring constantly. Reduce heat and simmer for 5 minutes. Remove from heat and stir in lemon juice. Cool.

Spoon this filling into the baked and cooled crust.

Topping:

1 cup sour cream
1 tbsp. sugar
1 tsp. vanilla extract

Mix sour cream, sugar and vanilla and spread over pie. Sprinkle with reserved crumbs. Serve.